In a process of forming a multilayer wiring structure of a semiconductor device, the following process is performed. For example, a SiCOH film that is a low dielectric constant film made of silicon (Si), carbon (C), hydrogen (H) and oxygen (O) is formed as an interlayer insulating film on a substrate, and a recess including a trench and a via hole is formed in the interlayer insulating film. Then, copper (Cu) is filled in the recess to form an upper layer side wiring connected to a lower layer side wiring. Further, in order to prevent copper from diffusing into the interlayer insulating film, for example, tantalum (Ta), tantalum nitride (TaN) or a laminated film thereof is used as a so-called barrier film between the copper wiring and the interlayer insulating film. In addition, titanium (Ti), titanium nitride (TiN) or a laminated film thereof is known as a barrier film.
When miniaturization of the line width of a copper wiring is advanced along with miniaturization of a pattern of a semiconductor device, an increase in wiring resistance or electrode resistance (via resistance) in a via hole affects the performance of the semiconductor device. In order to reduce the resistance of conductive paths (wiring and electrode), it is important to increase the volume of copper, to reduce the thickness of an adhesion layer or a barrier layer of the bottom of the via hole, and to suppress the via resistance by reducing the number of interfaces.
However, in the case of using the above-mentioned materials as a barrier film, when the line width of the recess is fine and an aspect ratio of the recess increases, the filling characteristics become poor. Also, it is disadvantageous that the resistance of the material itself is large.
From this point of view, the use of Ru with a small resistance and good filling characteristics, instead of the above-mentioned materials, as a barrier film has been proposed in U.S. Application Publication No. US2008/237860A1 (FIG. 1). FIGS. 22A to 22E are diagrams showing a process of forming the copper wiring in the case of using Ru as a barrier film. First, after a recess 2 including a trench and a via hole is formed in an interlayer insulating film (SiCOH film) 1 of the upper layer side (FIG. 22A), a base film 3 such as Ta or TaN described above is formed in the recess 2 (FIG. 22B), and a Ru film 4 is formed on the base film 3 (FIG. 22C). Then, copper (filling material made of copper) 5 is filled in the recess 2 (FIG. 22D), and excess copper 5 is removed by chemical mechanical polishing (CMP) to form a wiring structure of the upper layer side (FIG. 22E). Reference numerals 61 to 63 denote an interlayer insulating film, a copper wiring and a barrier layer, respectively. Reference numeral 64 denotes an etching stopper film (which performs a stopper function during etching) having a function of preventing diffusion of copper.
The reason that the base film 3 is interposed between the interlayer insulating film 1 and the Ru film 4 is as follows. In the SiCOH film that is the interlayer insulating film 1, bonds in the film are cut off by a plasma during etching or asking and C is eliminated from the film. Then, moisture or the like in the atmosphere is coupled to the dangling bonds generated by the elimination of C to form Si—OH. Thus, a surface portion becomes a damage layer. Since the content of C decreases in the damage layer, the relative permittivity increases. For this reason, the surface portion is removed by, for example, hydrofluoric acid. Thus, the surface state of the interlayer insulating film 1 immediately before the barrier film is formed becomes hydrophobic.
Meanwhile, since Ru has large Gibbs free energy of oxide formation, Ru is difficult to bond with O of the SiCOH film. Thus, a thin base film 3 made of Ta or the like and having small Gibbs free energy of oxide formation is thinly formed before the formation of the Ru film 4. In this case, since the Ru film 4 is used as a barrier film, it is less affected by high resistance or poor filling characteristics of the base film 3. However, since the base film 3 is interposed, in addition to the Ru film 4, between copper of the lower layer side and copper of the upper layer side at the bottom of the via hole, it is demanded to reduce the resistance of the conductive path, and further improvements are desired.
Further, in Japanese Patent Application Publication No. 2005-347472 (FIGS. 1 and 3), there is described a problem that when a SiCOH film is plasma etched, a portion of the film is bonded to a recess to generate nucleation of a seed such as methyl group or the like, and the film quality deteriorates when a barrier film is formed in this state. In order to solve this problem, there has been proposed a technique in which the SiCOH film is processed by a hydrogen plasma to remove methyl groups or the like on the surface of the recess and the bonds are terminated with H atoms. In this technique, the surface of the recess to be processed is hydrophilic, and this technique differs from the technique of the present invention.
In addition, in J. Vac. Sci. Technol. A 26(4), July/August 2008 pp. 974-979, there is described a method of forming amorphous alloy of Ru and phosphorus (P) on an insulating film directly without using a base film by chemical vapor deposition (CVD). However, it has also been demonstrated that the adhesion strength of Ru atoms at the interface of Cu is inferior to Cu—Ru bonds of a crystalline structure due to interposed P atoms.